External device access apparatus, control method thereof, and system lsi

Abstract

An external device access apparatus according to the present invention includes: an address control unit that accepts a prefetch request and a prefetch data readout request from a master and performs a prefetch operation and a prefetch data readout operation; a readout data storage unit that stores data read out through the prefetch operation; a storage operation status holding unit that holds a prefetch operation status indicating whether or not the prefetch operation has been completed; and an acceptance signal generation unit that outputs, to the master, an acceptance signal indicating that the prefetch data readout request has been accepted from the master. First information indicating a status of the prefetch operation is outputted to the master based on the prefetch operation status.

1 . An external device access apparatus that performs, in response to a request from a master, a prefetch operation of reading out data from an external device and a prefetch data readout operation of outputting the data read out through the prefetch operation to the master, said apparatus comprising:
 a control unit configured to accept a prefetch request and a prefetch data readout request from the master and perform the prefetch operation and the prefetch data readout operation;   a data storage unit configured to store the data read out through the prefetch operation;   a status holding unit configured to hold a prefetch operation status indicating whether or not the prefetch operation has been completed; and   an acceptance signal generation unit configured to output, to the master, an acceptance signal indicating that the prefetch data readout request from the master has been accepted,   wherein said control unit is configured to output the data stored in said data storage unit to the master as the prefetch data readout operation; and   said control unit is configured to output first information indicating a status of the prefetch operation to the master, the status being based on the prefetch operation status.   
     
     
         2 . The external device access apparatus according to  claim 1 ,
 wherein said acceptance signal generation unit is configured to output the acceptance signal to the master, regardless of whether or not the prefetch operation has been completed, when the prefetch data readout request is accepted by said control unit; and   said control unit is configured to output the first information to the master upon accepting the prefetch data readout request.   
     
     
         3 . The external device access apparatus according to  claim 1 ,
 wherein said control unit is configured to output the prefetch operation status to the master as the first information.   
     
     
         4 . The external device access apparatus according to  claim 1 ,
 wherein said external device access apparatus and the master are connected via a readout data bus; and   said control unit is configured to output the data stored in said data storage unit and the first information to the master via the readout data bus.   
     
     
         5 . The external device access apparatus according to  claim 4 ,
 wherein said control unit is configured to output the data stored in said data storage unit to the master via the readout data bus in the case where the prefetch operation status indicates that the prefetch operation has been completed, and output pre-set data as the first information to the master via the readout data bus in the case where the prefetch operation status indicates that the prefetch operation has not been completed.   
     
     
         6 . The external device access apparatus according to  claim 4 ,
 wherein said control unit is configured to output the data stored in said data storage unit to the master via the readout data bus in the case where the prefetch operation status indicates that the prefetch operation has been completed, and output an address of the external device, for which the readout is being performed through the prefetch operation, as the first information to the master via the readout data bus in the case where the prefetch operation status indicates that the prefetch operation has not been completed.   
     
     
         7 . The external device access apparatus according to  claim 1 ,
 wherein said control unit is further configured to accept a prefetch operation status readout request from the master; and   said control unit is configured to output the first information to the master in the case where the prefetch operation status readout request has been accepted.   
     
     
         8 . The external device access apparatus according to  claim 1 ,
 wherein the external device outputs a status signal indicating an operational status of the external device, and   said external device access apparatus further comprises:   a status signal storage unit configured to store the status signal at the point in time of the completion of the prefetch operation; and   a status signal output unit configured to output the status signal stored in said status signal storage unit to the master in the case where the prefetch operation status indicates that the prefetch operation has been completed, and output the status signal outputted by the external device to the master in the case where the prefetch operation status indicates that the prefetch operation has not been completed.   
     
     
         9 . The external device access apparatus according to  claim 1 ,
 wherein the external device outputs a status signal indicating an operational status of the external device, and   said acceptance signal generation unit is configured to selectively perform, when the prefetch data readout request has been accepted by said control unit and based on the status signal, a first operation that outputs the acceptance signal to the master regardless of whether or not the prefetch operation has been completed or a second operation that outputs the acceptance signal to the master after the prefetch operation has been completed.   
     
     
         10 . The external device access apparatus according to  claim 8 ,
 wherein said control unit is further configured to accept a prefetch stopping request from the master, and   said external device access apparatus further comprises   a prefetch stopping unit configured to stop the prefetch operation in the case where the prefetch stopping request has been accepted by said control unit.   
     
     
         11 . The external device access apparatus according to  claim 1 ,
 wherein the external device outputs a status signal indicating an operational status of the external device, and   said external device access apparatus further comprises   a prefetch stopping unit configured to stop the prefetch operation based on the status signal outputted by the external device in the case where the prefetch data readout request has been accepted by said control unit and the prefetch operation status indicates that the prefetch operation has not been completed.   
     
     
         12 . The external device access apparatus according to  claim 7 ,
 wherein the external device outputs a status signal indicating an operational status of the external device;   said external device access apparatus and the master are connected via a first signal bus; and   said external device access apparatus further comprises:   a status signal storage unit configured to store the status signal at the point in time of the completion of the prefetch operation;   a readout time status storage unit configured to store a readout time prefetch operation status that is the prefetch operation status at the point in time when the prefetch data readout request has been accepted by said control unit; and   a signal output unit configured to output the prefetch operation status to the master via the first signal bus in the case where the prefetch operation status indicates that the prefetch operation has not been completed, and output the status signal stored in said status signal storage unit to the master via the first signal bus in the case where the prefetch operation status indicates that the prefetch operation has been completed,   wherein said control unit is configured to output the readout time prefetch operation status to the master as the first information in the case where the prefetch operation status readout request has been accepted.   
     
     
         13 . The external device access apparatus according to  claim 1 ,
 wherein said acceptance signal generation unit is configured to selectively perform, when the prefetch data readout request has been accepted by said control unit, a first operation that outputs the acceptance signal to the master regardless of whether or not the prefetch operation has been completed or a second operation that outputs the acceptance signal to the master after the prefetch operation has been completed.   
     
     
         14 . The external device access apparatus according to  claim 13 ,
 wherein said acceptance signal generation unit is configured to selectively perform the first operation or the second operation, based on a control signal outputted by the master.   
     
     
         15 . The external device access apparatus according to  claim 13 ,
 wherein the prefetch data readout request includes a first prefetch data readout request and a second prefetch data readout request;   said control unit is configured to accept the first prefetch data readout request in the case where a first address has been outputted by the master, and accept the second prefetch data readout request in the case where a second address has been outputted by the master; and   said acceptance signal generation unit is configured to perform the first operation in the case where the first prefetch data readout request has been accepted by said control unit, and perform the second operation in the case where the second prefetch data readout request has been accepted by said control unit.   
     
     
         16 . The external device access apparatus according to  claim 13 , further comprising
 a status setting unit in which a first status or a second status is set,   wherein said control unit is further configured to accept a prefetch readout control operation request from the master;   said control unit sets the first status or the second status in said status setting unit as instructed by the master in the case where the prefetch readout control operation request has been accepted; and   said acceptance signal generation unit is configured to perform the first operation in the case where the first status is set in said status setting unit, and perform the second operation in the case where the second status is set in said status setting unit.   
     
     
         17 . The external device access apparatus according to  claim 1 , further comprising
 a count unit configured to, in the case where a prefetch data readout request has been accepted by said control unit while the prefetch operation is being executed, count the time from when the prefetch data readout request is accepted until the prefetch operation is completed,   wherein said control unit outputs the time counted by said count unit as the first information to the master.   
     
     
         18 . The external device access apparatus according to  claim 17 ,
 wherein said control unit is further configured to accept a time readout request from the master, and   said external device access apparatus further comprises   a time storage unit configured to store the time counted by said count unit,   wherein said control unit outputs the time stored in said time storage unit as the first information to the master in the case where a time readout request has been accepted.   
     
     
         19 . A system LSI comprising the external device access apparatus according to  claim 1  and a master,
 wherein said external device access apparatus outputs the first information as an interrupt signal or as a thread switching signal for said master, and   said master processes the first information as an interrupt or as a thread switching signal.   
     
     
         20 . A system LSI comprising the external device access apparatus according to  claim 1  and a master,
 wherein said external device access apparatus outputs the first information as a flag signal that can be processed by said master through software, and   said master processes the first information as a flag signal that can be processed through software.   
     
     
         21 . A system LSI comprising the external device access apparatus according to  claim 14  and a master,
 wherein said master outputs the control signal to said external device access apparatus in synchronization with the prefetch data readout request.   
     
     
         22 . A control method for an external device access apparatus that performs, in response to a request from a master, a prefetch operation of reading out data from an external device and a prefetch data readout operation of outputting the data read out in the prefetch operation to the master, said method comprising:
 accepting a prefetch request from the master;   reading out data from the external device and storing the read-out data in a data storage unit in the case where the prefetch request has been accepted;   holding a prefetch operation status indicating whether or not said storing has been completed;   accepting a prefetch data readout request from the master;   outputting, to the master, an acceptance signal indicating that the prefetch data readout request has been accepted in the case where the prefetch data readout request has been accepted;   outputting the data stored in said data storage unit to the master in the case where the prefetch data readout request has been accepted; and   outputting first information indicating a status of the prefetch operation to the master based on the prefetch operation status.